A process for producing a thermoplastic sandwich material that includes a honeycomb structure is disclosed in U.S. Pat. No. 5,683,782. Referring to FIG. 1 of U.S. Pat. No. 5,683,782, a greatly enlarged sectional representation of a honeycomb segment with a cover layer is shown. In accordance with the invention disclosed in this patent, a thermoplastic sandwich material is made from two outer reinforced thermoplastic skins with a cellular core at the center that is molded by a thermocompression process. The skins are formed from polypropylene with continuous glass mats or are formed by woven glass with polypropylene fibers. The content of U.S. Pat. No. 5,683,782 is incorporated by reference into this application as if fully set forth herein.
Thermoplastic sandwich materials such as those disclosed in U.S. Pat. No. 5,683,782 have been utilized in a variety of different applications. For example, U.S. patent application Ser. No. 09/451,970, filed Nov. 30, 1999 discloses a method for molding an impact resistant automotive part such as a bumper beam. A thermoplastic reinforced fiber structure at least partially forms a pair of attachment portions of the automotive part and continuously extends between the attachment portions to link the attachment portions. The content of the Ser. No. 09/451,970 patent application is incorporated by reference into this application as if fully set forth herein.
In another example, U.S. patent application Ser. No. 09/445,356, filed Dec. 10, 1999 discloses a method of making a composite panel that has a sandwich structure and that is provided with a hinge. The panel comprises a stack that includes at least one first skin of a reinforced thermoplastic material and a second skin of a thermoplastic material. The panel is formed by preheating the first and second skins to a softening temperature, and then pressing the stack of skins at a pressure that lies in a predetermined range. The content of the Ser. No. 09/445,356 patent application is incorporated by referenced into this application as if fully set forth herein.
Yet another exemplary use of thermoplastic sandwich material is disclosed in U.S. patent application Ser. No. 09/485,142, filed Feb. 4, 2000. This application discloses a method of making a reinforced composite panel of the sandwich type having a cellular-core. The content of the Ser. No. 09/485,142 application is incorporated by reference into this application as if fully set forth herein.
U.S. patent application Ser. No. 09/525,346, filed Mar. 15, 2000 discloses the utilization of thermoplastic sandwich material in a certain application. In particular, this application discloses a method and system for co-molding a thermoplastic material with a thermoplastic sandwich material to form a thermoplastic sandwich article. The article has a thermoplastic inner portion. The content of Ser. No. 09/525,346 patent application is incorporated by reference into this application as if fully set forth herein.
U.S. patent application Ser. No. 09/525,785 entitled "Method and System For Molding Thermoplastic Sandwich Material and Deep-Drawn Article Produced Thereby," filed Mar. 15, 2000 discloses a method and system for molding a thermoplastic sandwich material to form a deep-drawn article. In particular, an inner portion of a blank of thermoplastic sandwich material is forced into a female die along a vertical axis to form a deep-drawn article. A step of clamping may be performed at a plurality of spaced outer portions of the blank immediately adjacent the female die. The content of the above-referenced "Method and System" patent application is incorporated by reference into this application as if fully set forth herein.
In use of such processes to form 3-D deep-drawn articles from a thermoplastic sandwich material, sometimes visual defects such as puckering, wrinkling, and the like may occur in the finished article, especially at the comer areas of the article. Visual defects of this sort may render the article visually unacceptable for commercial purposes.
In some applications, carpet has been utilized as a surface finish to render the article usable for commercial purposes. However, carpet is not suitable for use as an exterior finish in every application. Furthermore, in an application where an article is deep-drawn to a relatively large size such as over 18 inches, prior processes for forming thermoplastic sandwich materials may not allow "Class A" surfaces to be defined on the article that are visually acceptable for commercial purposes.